Methods and apparatuses for transmitting a reference signal

ABSTRACT

Embodiments of the present disclosure relate to a method and apparatus of transmitting a reference signal and a method and apparatus of receiving a reference signal. In one embodiment of the present disclosure, the method of transmitting a reference comprises receiving a reference signal configuration indication, wherein reference signal resources are divided into at least two reference signal groups, and the reference signal configuration indication indicates a reference signal configuration including a reference signal group configuration; and transmitting the reference signal using a reference signal sequence in a reference signal group as indicated by the reference signal group configuration, wherein the reference signal sequence can be multiplexed with another layer or another user in different reference signal groups. With embodiments of the present disclosure, reference signals for different layers or users can be multiplexed in different reference signal groups and thus, more mu-users with unequal allocated bandwidths can be supported without significant channel estimation loss and Peak to Average Power Ratio (PAPR) loss.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.16/739,886, filed on Jan. 10, 2020, which is a Continuation Applicationof U.S. Pat. No. 10,594,454, issued on Mar. 17, 2020, which is aNational Stage of PCT/CN2016/071500, filed on Jan. 20, 2016.

FIELD OF THE INVENTION

Embodiments of the present disclosure generally relate to wirelesscommunication techniques and more particularly relate to a method andapparatus for transmitting a reference signal and a method and apparatusfor receiving a reference signal.

BACKGROUND OF THE INVENTION

Multi-antenna techniques can significantly increase the data rates andreliability of a wireless communication system. The performance is inparticular improved if both the transmitter and the receiver areequipped with multiple antennas, which results in a multiple-inputmultiple-output (MIMO) communication channel. Such systems and/orrelated techniques are commonly referred to as MIMO.

The Long Term Evolution (LTE) standard is currently evolving withenhanced MIMO support. A core component in LTE is support of MIMOantenna deployments and MIMO related techniques. Currentlyone-dimensional (horizontal) antenna array can provide flexible beamadaption in the azimuth domain only through the horizontal precodingprocess, while fixed down-tilt is applied in the vertical direction.

Recently, it has been found that the full MIMO capability can beexploited through leveraging two-dimensional (2D) antenna planar suchthat the user-specific elevation beamforming and spatial multiplexing onthe vertical domain are possible. Moreover, it was also proposed for theuplink (UL) demodulation reference signal (DMRS) to support additionalorthogonal ports for partially overlapping.

Besides, since the channel variation is slow in time domain if a highercenter frequency is used, the sparse RS can be used in time domain. Inother words, in the future 5G communication, only one or few symbols intime domain for RS transmission is proposed to reduce overhead, whereina Zadoff-Chu (ZC) sequence was proposed to be used in the new subframestructure. For purpose of illustration, FIG. 1 illustrates one ofpossible new subframe structures, in which there is only one symbol forRS transmission in one TTI. However, it shall be appreciated that inanother possible new subframe structure, the symbol may also be locatedin another position and/or it comprises more than one UL/DL symbol.

Thus, in the future 5G communication, it is possible to use only one offew symbols of DMRS for both UL and downlink (DL). In such a case, inorder to support higher order multi-user MIMO (MU-MIMO), it shallconsider using more orthogonal ports for partially overlapping BWs.

Therefore, in the art, a new DMRS design and new reference signaltransmission and receiving solutions are required so as to adapt for thenew subframe structure with the new channel characteristic variation inthe time domain and support more users or more layers.

SUMMARY OF THE INVENTION

In the present disclosure, there is provided a new solution forreference signal transmission and receiving to mitigate or at leastalleviate at least part of the issues in the prior art.

According to a first aspect of the present disclosure, there is provideda method of transmitting a reference signal. The method may comprisereceiving a reference signal configuration indication, wherein referencesignal resources are divided into at least two reference signal groups,and the reference signal configuration indication indicates a referencesignal configuration including a reference signal group configuration;and transmitting the reference signal using a reference signal sequencein a reference signal group as indicated by the reference signal groupconfiguration, wherein the reference signal sequence can be multiplexedwith another layer or another user in different reference signal groups.

In a second aspect of the present disclosure, there is provided a methodof receiving a reference signal. The method may comprise transmitting areference signal configuration indication, wherein reference signalresources are divided into at least two reference signal groups, and thereference signal configuration indication indicates a reference signalconfiguration including a reference signal group configuration; andreceiving the reference signal transmitted by using a reference signalsequence in a reference signal group as indicated by the referencesignal group configuration, wherein the reference signal sequence can bemultiplexed with another layer or another user in different referencesignal groups.

In a third aspect of the present disclosure, there is also provided anapparatus for transmitting a reference signal. The apparatus maycomprise an indication receiving module, configured for receiving areference signal configuration indication, wherein reference signalresources are divided into at least two reference signal groups, and thereference signal configuration indication indicates a reference signalconfiguration including a reference signal group configuration; and asignal transmission module, configured for transmitting the referencesignal using a reference signal sequence in a reference signal group asindicated by the reference signal group configuration, wherein thereference signal sequence can be multiplexed with another layer oranother user in different reference signal groups.

In a fourth aspect of the present disclosure, there is provided anapparatus of receiving a reference signal. The apparatus may comprise anindication transmission module, configured for transmitting a referencesignal configuration indication, wherein reference signal resources aredivided into at least two reference signal groups, and the referencesignal configuration indication indicates a reference signalconfiguration including a reference signal group configuration; and asignal receiving module, configured for receiving the reference signaltransmitted by using a reference signal sequence in a reference signalgroup as indicated by the reference signal group configuration, whereinthe reference signal sequence can be multiplexed with another layer oranother user in different reference signal groups.

According to a fifth aspect of the present disclosure, there is alsoprovided a computer-readable storage media with computer program codeembodied thereon, the computer program code configured to, whenexecuted, cause an apparatus to perform actions in the method accordingto any embodiment in the first aspect.

According to a sixth aspect of the present disclosure, there is furtherprovided a computer-readable storage media with computer program codeembodied thereon, the computer program code configured to, whenexecuted, cause an apparatus to perform actions in the method accordingto any embodiment in the second aspect.

According to a seventh aspect of the present disclosure, there isprovided a computer program product comprising a computer-readablestorage media according to the fifth aspect.

According to an eighth aspect of the present disclosure, there isprovided a computer program product comprising a computer-readablestorage media according to the sixth aspect.

With embodiments of the present disclosure, it provides a new solutionfor reference signal transmission and receiving, in which referencesignal resources are divided into at least two reference signal groupsand reference signals for different layers or users can be multiplexedin different reference signal groups. Thus, more mu-users with unequalallocated bandwidths can supported with significant channel estimationloss and Peak to Average Power Ratio (PAPR) problems.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present disclosure will become moreapparent through detailed explanation on the embodiments as illustratedin the embodiments with reference to the accompanying drawings,throughout which like reference numbers represent same or similarcomponents and wherein:

FIG. 1 schematically illustrates one of possible UL symbols in newlyproposed subframe structure with reduced UL symbols;

FIG. 2 schematically illustrates a DMRS pattern in the existingcommunication system;

FIG. 3 schematically illustrates a mapping of cyclicshift to n_(DMRS)⁽¹⁾ values;

FIG. 4 schematically illustrates a mapping of cyclic shift field inuplink-related DCI format to n_(DMRS,λ) ⁽²⁾ ⋅ and [w^(λ)(0) w^(λ)(1)];

FIG. 5 schematically illustrates a flow chart of a method oftransmitting a reference signal in accordance with one embodiment of thepresent disclosure;

FIGS. 6A and 6B schematically illustrate example DMRS patterns in afrequency division multiplexing (FDM) mode based on DMRS grouping inaccordance with one embodiment of the present disclosure;

FIG. 7 schematically illustrates an example DMRS pattern in a timedivision multiplexing mode (TDM) based on DMRS grouping in accordancewith one embodiment of the present disclosure;

FIGS. 8A to 8F schematically illustrate example possible DMRS patternsbased on DMRS grouping in further 5G communication system in accordancewith one embodiment of the present disclosure;

FIG. 9 schematically illustrates an example indication manner forindicating the DMRS group configuration in accordance with oneembodiment of the present disclosure;

FIG. 10 schematically illustrates another example indication manner forindicating the DMRS group configuration in accordance with anotherembodiment of the present disclosure;

FIG. 11 schematically illustrates a further example indication mannerfor indicating the DMRS group configuration in accordance with anotherembodiment of the present disclosure;

FIG. 12 schematically illustrates DMRS configurations for four new userequipment in accordance with one embodiment of the present disclosure;

FIG. 13 schematically illustrates DMRS signals transmitted in REs forUEi and UEj in accordance with one embodiment of the present disclosure;

FIG. 14 schematically illustrates DMRS configurations for legacy userequipment and two new user equipment in accordance with one embodimentof the present disclosure;

FIG. 15 schematically illustrate an example mapping of cyclic shiftfield in uplink-related DCI format n_(DMRS,λ) ⁽²⁾ ⋅ and [w^(λ)(0)w^(λ)(1)] in accordance with embodiments of the present disclosure;

FIG. 16 schematically illustrates a diagram of an example multipletransmission time interval (TTI) scheduling in accordance with oneembodiment of the present disclosure;

FIG. 17 schematically illustrates a diagram of another example multipleTTI scheduling in accordance in accordance with another embodiment ofthe present disclosure;

FIG. 18 schematically illustrate an example DMRS transmission based onthe staggering pattern in accordance in accordance with one embodimentof the present disclosure;

FIG. 19 schematically illustrates DMRS signals transmitted in fourresource elements for one OCC group in accordance with anotherembodiment of the present disclosure;

FIG. 20 schematically illustrates a flow chart of a method of receivinga reference signal in accordance with one embodiment of the presentdisclosure;

FIG. 21 schematically illustrates a block diagram of an apparatus fortransmitting a reference signal in accordance with one embodiment of thepresent disclosure;

FIG. 22 schematically illustrates a block diagram of an apparatus forreceiving a reference signal in accordance with one embodiment of thepresent disclosure; and

FIG. 23 further illustrates a simplified block diagram of an apparatus2310 that may be embodied as or comprised in UE and an apparatus 2320that may be embodied as or comprised in a base station in a wirelessnetwork as described herein.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, the solution as provided in the present disclosure will bedescribed in details through embodiments with reference to theaccompanying drawings. It should be appreciated that these embodimentsare presented only to enable those skilled in the art to betterunderstand and implement the present disclosure, not intended to limitthe scope of the present disclosure in any manner.

In the accompanying drawings, various embodiments of the presentdisclosure are illustrated in block diagrams, flow charts and otherdiagrams. Each block in the flowcharts or blocks may represent a module,a program, or a part of code, which contains one or more executableinstructions for performing specified logic functions, and in thepresent disclosure, a dispensable block is illustrated in a dotted line.Besides, although these blocks are illustrated in particular sequencesfor performing the steps of the methods, as a matter of fact, they maynot necessarily be performed strictly according to the illustratedsequence. For example, they might be performed in reverse sequence orsimultaneously, which is dependent on natures of respective operations.It should also be noted that block diagrams and/or each block in theflowcharts and a combination of thereof may be implemented by adedicated hardware-based system for performing specifiedfunctions/operations or by a combination of dedicated hardware andcomputer instructions.

Generally, all terms used in the claims are to be interpreted accordingto their ordinary meaning in the technical field, unless explicitlydefined otherwise herein. All references to “a/an/the/said [element,device, component, means, step, etc.]” are to be interpreted openly asreferring to at least one instance of said element, device, component,means, unit, step, etc., without excluding a plurality of such devices,components, means, units, steps, etc., unless explicitly statedotherwise. Besides, the indefinite article “a/an” as used herein doesnot exclude a plurality of such steps, units, modules, devices, andobjects, and etc.

Additionally, in a context of the present disclosure, a user equipment(UE) may refer to a terminal, a Mobile Terminal (MT), a SubscriberStation (SS), a Portable Subscriber Station (PSS), Mobile Station (MS),or an Access Terminal (AT), and some or all of the functions of the UE,the terminal, the MT, the SS, the PSS, the MS, or the AT may beincluded. Furthermore, in the context of the present disclosure, theterm “BS” may represent, e.g., a node B (NodeB or NB), an evolved NodeB(eNodeB or eNB), a radio header (RH), a remote radio head (RRH), arelay, or a low power node such as a femto, a pico, and so on.

Hereinafter, a DMRS pattern and mappings in the existing communicationsystem will be first described with reference to FIGS. 2 to 4 , for abetter understanding of the present disclosure.

Reference is first made to FIG. 2 , which illustrates a DMRS pattern inthe existing communication system in more detail. In the existingcommunication system, physical uplink sharing channel (PUSCH) is basedon Zadoff-Chu sequence. As illustrated in FIG. 2 , for UE i, signalsR_(i)(n) and R′_(i)(n) are DMRS sequence in the first slot and thesecond slot respectively and they may have different cyclic shifts.Signals R_(i)(n) and R′_(i)(n) may have the same root sequence if thesequence group hopping is disabled. In addition, two users transmittingsignals in MU-MIMO (referred to as mu-user hereinafter) with unequalbandwidth can use different OCC sequences in the two slots and aplurality of mu-users with equal bandwidth can use different cyclicshift in DMRS.

In the existing communication, the reference signal sequence r_(u,v)^((α))(n) is defined by a cyclic shift α of a base sequence r _(u,v)(n)according tor _(u,v) ^((α))(n)=e ^(jαn) r _(u,v)(n), 0≤n<M _(sc) ^(RS)Where n=0, . . . , M_(sc) ^(RS)−1, M_(sc) ^(RS)=mN_(sc) ^(RB) is thelength of the reference signal sequence and 1≤m≤N_(RB) ^(max,UL).Multiple reference signal sequences are defined from a single basesequence through different values of α. The Base sequences, r _(u,v)(n)are divided into groups, where u∈{0, 1, . . . , 29}; is the groupnumber, v is the base sequence number within the group, such that eachgroup contains one base sequence (v=0) of each length M_(sc)^(RS)=mN_(sc) ^(RB), 1≤m≤5 and two base sequences of each length M_(sc)^(RS)=mN_(sc) ^(RB), 6≤m≤N_(RB) ^(max,UL). The sequence group number uand the number v within the group may vary in time and the definition ofthe base sequence r _(u,v)(0), . . . ,r _(u,v)(M_(sc) ^(RS)−1) dependson the sequence length M_(sc) ^(RS).

In addition, the PUSCH demodulation signal sequence r_(PUSCH) ^((λ))(⋅)associated with layer λ is defined by

r_(PUSCH)^((λ))(m ⋅ M_(sc)^(RS) + n) = w^((λ))(m)r_(u, v)^((α_(λ)))(n)where

-   -   m=0, 1    -   n=0, . . . , M_(sc) ^(RS)−1        and        M _(sc) ^(RS) =M _(sc) ^(PUSCH)        The sequence r_(u,v) ^((α) ^(λ) ⁾(0), . . . , r_(u,v) ^((α) ^(λ)        ⁾(M_(sc) ^(RS)−1) is r _(u,v)(0), . . . , r _(u,v)(M_(sc)        ^(RS)−1) as described hereinbefore, and for DCI format 0, the        orthogonal sequence w^((λ))(m) is given by        [w ^(λ)(0)w ^(λ)(1)]=[1 1].        The cyclic shift α_(λ) in slot n_(s) is given as        α_(λ)=2πn_(cs,λ)/12 with        n _(cs,λ)=(n _(DMRS) ⁽¹⁾ +n _(DMRS,λ) ⁽²⁾ +n _(PN)(n _(k)))mod        12        where the values of n_(DMRS) ⁽¹⁾ is given by Table 5.5.2.2.2-2        of 3GPP TS 36.212, which is illustrated in FIG. 3 , according to        the parameter cyclicshift provided by higher layers. n_(DMRS,λ)        ⁽²⁾ is given by the cyclic shift for DMRS filed in most recent        uplink-related DCI in 3GPP TS 36.212 for the transport block        associated with the corresponding PUSCH transmission.        Particularly, the value of n_(DMRS,λ) ⁽²⁾ ⋅ is given in Table        5.5.2.1.1-1 3GPP TS 36.212, which is illustrated in FIG. 4 . The        quantity n_(PN)(n_(s)) is related to the slot and is given by

${n_{PN}\left( n_{s} \right)} = {\sum_{i = 0}^{7}{{c\left( {{8{N_{symb}^{UL} \cdot n_{s}}} + i} \right)} \cdot 2^{i}}}$where the pseudo-random sequence c(i) is defined by clause 7.2 in 3GPPTS 36.212 and the application of c(i) is cell-specific.

Hereinbefore, the DMRS pattern and mappings used in the existingcommunication system are described and for more details, one can referthe related content for example in 3GPP TS 36.211

In addition, as mentioned hereinbefore, in a case that only one or fewsymbols of DMRS is used for both UL and downlink (DL), in order tosupport higher order multi-user MIMO(MU-MIMO), it shall consider usingmore orthogonal ports for partially overlapping BWs. However, in exitingcommunication system, it only supports two multi-users with unequalallocated bandwidths, or it requires much standard effort and too muchrestriction on length of ZC sequences and cause Peak to Average PowerRatio (PAPR) issues. Thus, a new RS pattern and new RS transmission andreceiving solutions are provided in the present disclosure, which willbe described in detail with reference to FIGS. 5 to 23 .

FIG. 5 schematically illustrates a flow chart of a method oftransmitting reference signal in accordance with one embodiment of thepresent disclosure. As illustrated in FIG. 5 , first at step 510, areference signal configuration indication is received, wherein referencesignal resources are divided into at least two reference signal groups,and the reference signal configuration indication indicates a referencesignal configuration including a reference signal group configuration.

In embodiments of the present disclosure, RS resources, i.e., basicsequence for RS, can be divided into M different groups and the Mdifferent groups can be used either in frequency division mode or intime division mode to support more users or more layers. Next, exampleswill be given to explain it in more details and in those examples, DMRSresources are dived into two groups, i.e., M is equal to 2, for easyunderstanding; however, the skilled in the art can readily know that thenumber of M is not limited to 2 and can be any suitable number.

In FIG. 6A, DMRS resources are dived into two groups, DMRS group 0 andDMRS group 1, resource elements (REs) for carrying DMRS group 0 and REsfor carding DMRS group 1 are staggered in the frequency domain. Thus,for one DMRS port/layer, the length of DMRS sequence is half of thelength of PUSCH or the legacy DMRS sequence which is not transmittedwith the DMRS grouping as proposed herein. Thus, the number of resourceblocks (RB) allocated to new UE using the DMRS grouping shall bemultiple of M (i.e., 2). For example, in a case of M=2, the numbers ofthe RB shall be 2, 4, 6, etc. Alternatively, this condition may onlyneed to be satisfied when the number of RBs is less than 6.

FIG. 6B illustrates an example DMRS pattern in the frequency divisionmultiplexing mode based on DMRS grouping in accordance with oneembodiment of the present disclosure. The difference between the DMRSpattern as illustrated in FIG. 6A and that as illustrated in FIG. 6Blies in that reference signal groups are hopped in different symbols. Inother words, in the DMRS symbol in slot 0 and in the DMRS symbol in slot1, REs for carrying DMRS group 0 and REs for carrying DMRS group 1 arestaggered in the frequency domain in different ways. In the DMRS symbolin slot 0, REs for carrying DMRS group 0 and REs for carrying DMRS group1 are staggered in an order of DMRS group 0, DMRS group 1, DMRS group 0,DMRS group 1 . . . , while in the DMRS symbol in slot 1, REs forcarrying DMRS group 0 and REs for carrying DMRS group 1 are staggered inan order of DMRS group 1, DMRS group 0, DMRS group 1, DMRS group 0 . . ..

FIG. 7 illustrates a further example DMRS pattern based on DMRS groupingin further 5G communication system in accordance with one embodiment ofthe present disclosure. As illustrated in FIG. 7 , the New DMRS patteris achieved based on DMRS grouping but in time division multiplexingmode. That is to say, in the DMRS symbol in the slot 0, all REs arecarrying DMRS group 0, while in the DMRS symbol in slot 1, all REs arecarrying DMRS group 1.

As a matter of the fact, in the future 5G communication system, theframe structure may also have another form. It can be seen that in thefuture 5G communication system, the TTI length may be very short, andthus it may include for example two, or four consecutive DMRS symbols ina slot as illustrated FIG. 8A to FIG. 8E. In addition, the M is notlimited to 2, it can also be 3 or higher, as illustrated in 8F in FIG. 8.

Regarding whether the legacy DMRS pattern or new DMRS pattern is used,or in other word, whether the DMRS group configuration is enabled, itcan be informed by a bit in DRMS configuration Indication (DCI) formatinformation or radio resource control (RRC) signaling. The DMRS groupconfiguration for different UE or different layers of the UE can beindicated by a RS signal indication, which might be a RRC signaling orDCI format information explicitly or implicitly. That is to say, theDMRS group configuration can be indicated by a new RRC signaling, or beindicated by the DCI format which also indicates a cyclic shiftconfiguration and an orthogonal cover code configuration. As an example,the reference signal group configuration can be implicitly indicated bythe cyclic shift configuration. As another example, the reference signalgroup configuration can be explicitly indicated by a bit in thereference signal configuration indication.

In addition, the RRC signaling for the DMRS group configuration can be aseparate signaling from the RRC signaling for indicating whether the newDRMS pattern is enabled, or alternatively, whether the new DRMS patternis enabled and the DMRS group configuration can be indicated in the sameRRC signaling. Moreover, the same or different bit in DCI formatinformation can also be used to provide the DMRS group indication and anindication about whether the new DRMS is enabled.

In one embodiment of the present disclosure, only one reference groupcan be used by one UE. In such a case, the DMRS group configuration canbe indicated implicitly by the cyclic shift configuration, i.e., thecyclic shift field in DCI format. For example in FIG. 9 , a part ofindices in CS field of DCI format are for the new DMRS pattern, and theremaining part of indices in CS field of DCI format are for the legacyDMRS pattern. In other word, in the table for CS field in DCI for theNew UEs, all indices are divided into two part, a first part is toindicate to UE that it should use the legacy DMRS pattern, the secondpart is to indicate to UE that it should use the new DMRS pattern. Inthe second part, the indices are further divided into two portions, oneis for DMRS group 0 and the other is for DMRS group 1 (if M=2). Forexample, as illustrated in FIG. 9 , if the index in DCI format is 000,the UE should use new DMRS group 0 of new DMRS pattern to transmit DMRS;on the other hand, if the index in DCI format is 010, the UE should usethe legacy DMRS pattern. In such case, it does not need any RRCsignaling or any bit DCI information to indicate the new UE whether thelegacy pattern or the new pattern is used.

FIG. 10 schematically illustrates another example indication manner forindicating the DMRS group configuration in accordance with anotherembodiment of the present disclosure, wherein indices in CS field of DCIformat are divided into M parts (M=2). As illustrated in FIG. 10 ,indices in CS field of DCI format are divided into two parts, one partis for DMRS group 0, and the other part is for DMRS group 1. Forexample, indices 000,001,010,111 are included the first group, i.e.,DMRS group 0, and indices 011,100,101,110 are included in the secondgroup, i.e., DMRS group 1. Alternatively, it is also possible to dividecyclicshift (i.e., n_(DMRS) ⁽¹⁾ values as shown in FIG. 4 ) into Mgroups based on RRC signaling. As an example, indices 0, 1, 2, 3correspond to DMRS group 0, and the remaining indices correspond to DMRSgroup 1. In such case, it may use one-bit RRC signaling or one bit DCIinformation to indicate whether the legacy pattern or the new pattern isused.

In another embodiment of the present disclosure, more than one referencesignal group is allowed to be used by one user equipment. In this case,DMRS sequences for different layers of one UE can be multiplexed indifferent DMRS groups and it is possible to use new mapping table, whichmay be informed by an RRC signaling or one bit in DCI format. Theexample new table is illustrated in FIG. 11 , wherein Δ_(TC) indicatethe DMRS group configuration, the value of 0 indicates DMRS group 0; thevalue of 1 indicates DMRS group 1. From FIG. 11 , it is clear that theDMRS group configuration is bound with the CS index and the layer. Insuch a case, 4 UEs each with 2-layer can be scheduled in the followingway, fields 000+001+010+011 are used, the multiplexing is implemented bymeans of intra UE CS, inter UE OCC and FDM.

In a case that different layers in one UE can be multiplexed bydifferent DMRS groups, two layers can be supported with OCC or FDM, forexample, field 100 or 101 with FDM, or field 110 or 111 with OCC. At thesame time, in single user (SU) mode, it may support up to 8 layers. Inthis case, since UE needs to be configured with the layer number, the UEcan be implicitly informed of the DMRS, OCC and, FDM. As an example, ifUE is configured with 8-layer, and field 000 UE can assume thepre-defined mapping to be: for layer 0-3, CS and OCC, Δ_(TC) are shownin table; for layer 4-7, CS and OCC is same with layer 0-3 but with(1−Δ_(TC)) for FDM configuration.

In a further embodiment, for SU-MIMO with 4 or more layers, CS, OCC andDMRS group configurations can be implicitly informed to the UE. In sucha case, it is possible to use an aggregated reference signalconfiguration to support more layers in transmitting DMRS. Theaggregated reference signal configuration indicates a reference signalconfiguration aggregated from more than one configuration. For example,the aggregated reference configuration may be formed by aggregating thereference signal configuration indicated by the reference signalconfiguration indication and another reference signal configurationpredetermined to be used therewith. The another reference signalconfiguration may be a configuration which is obtained from thereference signal configuration indicated by the reference signalconfiguration indication but with a different reference signal groupconfiguration. Or alternatively, it may be a reference signalconfiguration in a cyclic field mapping table, which is different fromthe reference signal configuration indicated by the reference signalconfiguration indication and is pre-predetermined to be used with thereference signal configuration indicated by reference signalconfiguration indication. For example, for a layer number v, it may usethe same CS/OCC for the first v/2 layers and the second v/2 layers butwith different DMRS group configuration therefor. Thus, in thisembodiment, even if the reference signal configuration indication onlyindicates one reference signal configuration, it will aggregate two ormore CS/OCC/DMRS group configurations to support more layers (up to 8layers if a case M=2).

As an example, in the legacy table as illustrated in FIG. 3 , twoindices (i.e., two configurations) of the CS field are configured to oneUE to indicate CS and OCC configurations for 8 layers. The relationbetween the two indices can be fixed or predetermined, which can beinformed to the UE by using the legacy CS field in DCI format. Forexample, for 8 layers, index 000 actually represents indices 000 and 001which indicates CS/OCC for the first 4 layers and the second 4 layersrespectively, wherein the layer 0, 1, 2 and 3 use CS 0, 6, 3, 9 and OCC[1 1] [1 1] [1−1] [1 −1], and the layer 4, 5, 6, 7 use CS 6 0 9 3 andOCC [1 −1] [1 −1] [1 1] [1 1]. Or alternatively, the index 000 can beused to indicate CS/OCC for the even layers, e.g. 0, 2, 4, 6, and theindex 001 can be used to indicate CS/OCC for odd layers, e.g. 1, 3, 5,7.

Next, reference is made back to FIG. 5 and as is seen, at step 520, thereference signal is transmitted using a reference signal sequence in areference signal group as indicated in the reference signal groupconfiguration, wherein the reference signal sequence can be multiplexedwith another layer or another user in different reference signal groups.

After receiving the reference signal configuration information, the UEcan transmit the DMRS sequence according to the configurations asindicated in the reference signal configuration information.

Taking 4 one-layer UE as an example, UE0, UE1, UE2, UE3 are configuredwith indices 000, 001, 100 and 101 respectively in DCI format. FIG. 12illustrates the CS configurations, the OCC configurations and DMRSsignals transmitted in slot 0 or slot 1 when four new UE are paired. Inthe current standard, if the sequence group hopping is disabled, thecyclic shift offset between R′i and Ri should be identical for all theseUE in order to support MU-MIMO, i.e. R′i(n)=e^(jan) R_(i)(n). In otherword, cyclic shift index offset (or after mode 12) between two slots issame for all mu-users. For example, for UE0, cyclic shift indices inslot 0 and 1 are 0 and 6 respectively, the index offset value is 6; forUE3, the index in two slots is 8 and 2 respectively and the offset aftermod 12 is also 6.

FIG. 13 illustrates reference signals transmitted by two UE using newDMRS format in two slots wherein the closest four REs, i.e., the firsttwo reference signals in slot 0 and slot 1 are further illustrated atbottom for a purpose of clarification. The symbols in the closest fourREs can be given by the following expression:

$\begin{bmatrix}{R_{0}(n)} & {e^{jan}R_{0}(n)} & 0 & 0 \\{R_{1}(n)} & {{- e^{jan}}{R_{1}(n)}} & 0 & 0 \\0 & 0 & {R_{2}(n)} & {e^{jan}R_{2}(n)} \\0 & 0 & {R_{3}(n)} & {{- e^{jan}}R_{3}(n)}\end{bmatrix}$

Form the above expression, it can be seen that for two new UE, theorthogonality can be achieved between these four UE even they haveunequal bandwidth.

However, when legacy UE is paired with new UE, it cannot achieve theorthogonality since they use different DMRS pattern and the legacy UE isnot multiplexed in different DMRS groups. In other words, for the samefrequency resources, the length of legacy DMRS sequence is 2 times ofthat of new DMRS sequence. Therefore, basically, the resource index oflegacy DMRS sequence is 2 times of the new DMRS sequence if the startfrequency positions of legacy UE and new UE are same. FIG. 14illustrates an example of the CS configurations, the OCC configurationsand DMRS signals transmitted in slot 0 or slot 1 when the legacy UE ispaired with new UEs. The symbols in the closest four REs can be given bythe following expression:

$\begin{bmatrix}{R_{0}\left( {2n} \right)} & {e^{jan}{R_{0}\left( {2n} \right)}} & {R_{0}\left( {{2n} + 1} \right)} & {e^{{ja}({{2n} + 1})}{R_{0}\left( {{2n} + 1} \right)}} \\{R_{1}(n)} & {{- e^{jan}}{R_{1}(n)}} & 0 & 0 \\0 & 0 & {R_{2}(n)} & {{- e^{jan}}{R_{2}(n)}}\end{bmatrix}$

From the expression, it is clear that the orthogonality cannot beachieved. In fact, in order to achieve the orthogonality, the cyclicshift offset between two slots for New UE should be 2 times of legacyones. In other words, excluding the OCC sequence, the phase shiftbetween two slots should be kept as legacy ones, i.e. R′₁/R₁=R′₀/R₀ inthe same frequency resource n. Thus, in such a case, it is required toincrease a cyclic shift offset between slots for new user equipmenttransmitting the reference signal, to improve orthogonality between thenew user equipment and legacy user equipment.

In one embodiment of the present disclosure, the cyclic shift ismagnified by M when the DMRS sequence is generated. For example, forDMRS group 0, reference signal sequence can be changed as:r _(u,v) ^((α))(n)=e ^(jα2n) r _(u,v)(n), 0≤n<M _(sc) ^(RS),For DMRS group 1, reference signal sequence can be changed into:r _(u,v) ^((α))(n)=e ^(jα(2n+1)) r _(u,v)(n), 0≤n<M _(sc) ^(RS)wherein MR_(sc) ^(RS) is the DMRS sequence length. Therefore, if thesame frequency resources are allocated to legacy UE₀ and the new UE1,the DMRS sequence length of UE₁ is half of that of UE₀.

After changing the DMRS sequence as proposed, the new symbols in theclosest four REs can be given by the following expression:

$\begin{bmatrix}{R_{0}\left( {2n} \right)} & {e^{{ja}2n}{R_{0}\left( {2n} \right)}} & {R_{0}\left( {{2n} + 1} \right)} & {e^{{ja}({{2n} + 1})}R0\left( {{2n} + 1} \right)} \\{R_{1}(n)} & {{- e^{{ja}2n}}{R_{1}(n)}} & 0 & 0 \\0 & 0 & {R_{2}(n)} & {{- e^{{ja}({{2n} + 1})}}{R_{2}(n)}}\end{bmatrix}$

From the above expression, it can be seen that the orthogonality can begot between the legacy UE and the new UE.

However, in the new DMRS sequence, it can also be seen that theorthogonality between difference CSs is broken. For example,orthogonality between CS0 and CS 6 has broken. In the existing DMRSconfiguration, the cyclic shift offset is 6, and two closest REs infrequency domain can be one orthogonal group in the legacy patterns.That is to say in the frequency domain, this can be translated into anorthogonal frequency-code spanning blocks of 2 consecutive sub-carriers.Consequently, the granularity of channel estimates is (approximately)one per 2 sub-carriers. After increasing cyclic shift offset when theDMRS sequence is generated, this cannot be guaranteed.

In the embodiment wherein the cyclic shift offset is increased, theorthogonality of CS offset 3 leads to orthogonal frequency-code spanningblocks of 2 consecutive DMRS sub-carriers. In addition, two CSs whichhave 6 offsets will lead to same DMRS sequence.r _(u,v) ^((α))(n)=e ^(jα2n) r _(u,v)(n), 0≤n<M _(sc) ^(RS) =>r _(u,v)^((α))(n)=r _(u,v) ^((α+6))(n)Therefore, in the new DMRS pattern, CS offset 3 should be used insteadof 6. In such a case, the cyclic shift for the new user equipment can bedecreased to keep the orthogonality between different cyclic shifts. Insuch a case, it may consider to shrink n_(DRMS) ⁽¹⁾ and/or n_(DRMS,λ)⁽²⁾. That is to say, the equation of n_(cs,λ) can be changed asn _(cs,λ)=((n _(DMRS) ⁽¹⁾ +n _(DMRS,λ) ⁽²⁾)/2+n _(PN)(n _(s)))mod 12orn _(cs,λ)=(n _(DMRS) ⁽¹⁾ +n _(DMRS,λ) ⁽²⁾/2+n _(PN)(n _(s)))mod 12As another option, the new cyclic shift values can be introduced.Especially for up to two layers, the CS offset between the first layerand the second layer should be 3. For example, it is possible to revisethe related values 0, 6 to be 0, 3 which corresponds to index 000 intable 5.5.2.1.1.−1 of GPP TS 36.212. FIG. 15 schematically illustratesan example mapping of cyclic shift field in uplink-related DCI format ton_(DRMS,λ) ⁽²⁾ and [w^(λ)(0) w^(λ)(1)] in accordance with embodiments ofthe present disclosure. In such a case, it may use the old equation ofn_(cs,λ) or just using mode 6, as illustrated as below:n _(cs,λ)=((n _(DMRS) ⁽¹⁾ +n _(DMRS,λ) ⁽²⁾)+n _(PN)(n _(s)))mod 6orn _(cs,λ)=((n _(DMRS) ⁽¹⁾ +n _(DMRS,λ) ⁽²⁾)+n _(PN)(n _(s)))mod 12

As an example, one bit DCI formation or a RRC signal may be used toindicate whether the new DMRS pattern/sequence or legacy DMRSpattern/sequence is to be used. If it is new one, the CS offset betweenthe second layer and the first layer is 3. Since the CS offset ismagnified by a factor of M, related DMRS sequences derived from indices000 and 001 are the same, related DMRS sequences from indices 010 and111 are the same, related DMRS sequences from indices 011 and 110 arethe same, and related DMRS sequences from indices 100 and 101 are alsothe same. Therefore, the whole CS indices can be divided into 2 groups,one group corresponds to one DMRS group and have different related DMRSsequences. For example, indices 000, 010, 011, 100, 101 can correspondto DMRS group0, the remaining indices may correspond to DMRS group 1. Insuch a way, when UE receives index 000, it means the UE belongs to DMRSgroup 0.

In addition, considering backward compatibility, the phase shift betweentwo slots of one subframe for new UEs shall keep same with legacy ones.

For DMRS group 0, reference signal sequence can be kept intact withlegacy formula:r _(u,v) ^((α))(n) =e ^(jαn) r _(u,v)(n), 0≤n<M _(sc) ^(RS)while for DMRS group 1,

${{r_{U,V}^{(_{\alpha})}(n)} = {e^{j\frac{\alpha}{2}}e^{j\alpha n}{{\overset{\_}{r}}_{U,V}(n)}}},{0 \leq n < M_{sc}^{RS}}$n _(cs,λ)=(n _(DMRS) ⁽¹⁾ +n _(DMRS,λ) ⁽²⁾+2n _(PN)(n _(s)))mod 12

Thus, in this solution, the cyclic shift offset between two slots of onesubframe for new UEs also is kept M times of legacy ones.

In addition, it can be seen that in further 5G communication system, theTTI might be very short. In scenarios with a very short TTI length, theDMRS can be removed in some TTIs. In other word, the DMRS is nottransmitted in every TTI. In this case, 1 bit or few bits in physicalcontrol signaling can used to inform UE how many DMRS symbols are used,or whether there is DMRS symbols in current TTI. If there is no DMRS ina TTI, the UE can use the previous DMRS to demodulate data. In addition,a retransmission without the DMRS can be performed by using the DMRS inprevious transmission or initial transmission.

In addition, it may also consider multiple TTI scheduling. In otherwords, eNB only configures control signaling information in one TTI, andUE can receive or/and transmit data in multiple TTI based on the controlsignaling information. Thus, in such a case, it is possible that onlyone or few TTI includes DMRS. As another option, OCC sequences with Llength can be used, which is illustrated in FIG. 16 As illustrated, OCCsequences or DFT sequences with a length of L can be applied in the DMRSfor these L TTIs. In this case, there is only one DMRS in each of TTIs.Taking. L=4 as an example, four orthogonal OCC sequences can bemultiplexed on the DMRS sequence. In this way, maximum 4 layers or 4mu-users can be multiplexed by OCC sequences.

As a further option, it is also possible to use 6 DFT sequences asillustrated in FIG. 17 In such a case, it may transmit two DMRSsequences in each TTI and DFT sequence value can be multiplexed on theDMRS sequence in each TTI. Thus, maximum 6 layers or users can bemultiplexed by 6 DFT sequences.

In another different embodiment, each user or layer can be transmittedby using M DMRS group in a staggering pattern. In other word, one UEwill transmit multiplex DMRS sequences using M DMRS groups based on thestaggering pattern. In this embodiment, UE needs to transmit DMRSsequences in each DMRS group for every layer. In such a case, differentUE can be multiplexed by different OCC sequences.

For example, in a case that only one symbol is used for DMRStransmission as illustrated in FIG. 18 both UE₀ and UE₁ transmitreference signal sequences using M DMRS groups in the staggering patternand the two UE transmits the reference signals in MU-MIMO mode withOCC=2 in the same one symbol, wherein [w₀₀ w₀₁]32 [1 1] and [w₁₀ w₁₁]=[1−1]. In such case, UE₀ with one layer transmits DMRS sequence w₀₀*R₀ inDMRS group 0 and DMRS sequence w₀₁*R′₀ in DMRS group1 and meanwhile inthe same symbol, UE₁ transmits DMRS sequence w₁₀*R₁ in DMRS group 0 andDMRS sequence w₁₁*R′₁ in DMRS group1. In another case that two symbolsare used for DMRS transmission as illustrated in FIG. 19 , for examplein R10 uplink DMRS pattern, for UE i, four ZC sequences with differentCS R⁰i R¹i R²i R³i can be used and in such a way, it can extend R10uplink MU-MIMO mechanism with OCC=4 in order to support 4 MU-users,wherein UEs can be scheduled with different bandwidths. In such a case,the OCC may be:

$\begin{matrix}{{\left\lbrack {w_{i0}w_{i1}w_{i2}w_{i3}} \right\rbrack = \begin{bmatrix}1 & 1 & 1 & 1\end{bmatrix}};{or}} \\{\begin{bmatrix}1 & {- 1} & 1 & {- 1}\end{bmatrix};{or}} \\{\begin{bmatrix}1 & 1 & {- 1} & {- 1}\end{bmatrix};{or}} \\{\begin{bmatrix}1 & {- 1} & {- 1} & 1\end{bmatrix}.}\end{matrix}$

In shall be noticed that in the embodiment wherein each user or layercan be transmitted by using M DMRS groups in the staggering pattern, theDMRS sequence can also be changed to have backward compatibility to keepthe orthogonally between the new UE and legacy and between different CSsjust as described hereinabove. In other word, for all UEs, the cyclicshift offset between the four ZC sequences should be kept same.Particularly, for UE i, the cyclic shift offset between R¹ _(i) and R²_(i) can be same as the offset between R¹ _(j) and R² _(j) for UEj whichare co-scheduled with UEi in one TTI. In the meanwhile, when new UEmultiplexing with legacy UE, the cyclic shift offset between the DMRSsequences in two slots should be same as legacy ones as well.

In addition, it is also possible to use further schemes to improve thetransmission performance. For example, in a case DMRS groups is enabled,the power in one DMRS RE will be two times than that in PUSCH, if powerof DMRS symbols and that of PUSCH symbols are kept same in one TTI.Moreover, the power of DMRS symbols will be half of that in PUSCH symbolif power of one DMRS RE and that of one PUSCH RE is kept same. All thesemeans power imbalance between different symbols. Therefore, it maychange the scaling factor to avoid the power imbalance.

Therefore, in the section 5.5.2.1.2 of 3GPP TS 36.213, the amplitudescaling factor can be changed as delta*β_(PUSCH), wherein delta can be1, or sqrt(2) which can be informed to UE as default information. As anexample, for UEs with New DMRS pattern, the amplitude scaling factorwill be delta*β_(PUSCH). Alternatively, cNB can use RRC signaling toinform UE of the delta values, and eNB can choose one value frommultiple values for UE. For example, the candidate delta values can be{1, sqrt(2)} or {1, sqrt(2), sqrt(0.5), et.}. In such a way, powerimbalance can be alleviated greatly.

Hereinbefore, description is mainly made to the solution of referencesignal transmission. In the present disclosure, there is also provided amethod of receiving reference signal which will described with referenceFIG. 20 .

As illustrated in FIG. 20 , the method 2000 may start from step 2010, inwhich a reference signal configuration indication is transmitted.Particularly, as described hereinbefore, reference signal resources candivided into at least two reference signal groups, and the referencesignal configuration indication can indicate a reference signalconfiguration including a reference signal group configuration.

In an embodiment of the present disclosure, the reference signalresource can be divided into at least two reference signals and the atleast two reference signal groups are multiplexed either in a frequencydivision multiplexing mode or in a time division multiplexing mode andin such a way, it can support more users or more layers with limitedantenna port resources. In addition, in a frequency divisionmultiplexing mode, the at least two reference signal groups can befurther hopped in different symbols.

In another embodiment of the present disclosure, reference signalconfiguration indication may further indicate a cyclic shiftconfiguration and an orthogonal cover code configuration in addition tothe reference signal group configuration. This means that the cyclicshift configuration, the orthogonal cover code configuration and thereference signal group configuration can be indicated by the samereference signal indication, i.e., DCI format. For example, thereference signal group configuration may be implicitly indicated by thecyclic shift configuration, or alternatively explicitly indicated by abit in reference signal configuration indication. In addition, whetherthe reference signal group configuration is enabled can also beindicated by a bit in reference signal configuration indication or byusing a separate RRC signaling.

In some embodiments of the present disclosure, only one reference signalgroup is allowed to be used by one user equipment. In such a case, apart of indices for the cyclic shift configuration can be reserved for alegacy reference signal pattern, and a remaining part of the indices aredivided to at least two groups, each of which is allocated acorresponding one of the at least two reference signal groups. Oralternatively, indices for the cyclic shift configuration can be dividedinto at least two groups, each of which is allocated a corresponding oneof the at least two reference signal groups.

In some embodiments of the present disclosure, more than one referencesignal group is allowed to be used by one user equipment. In such acase, the reference signal group indication can be bound with indicesfor the cyclic shift. In other words, for a specific index for thecyclic shift, the reference signal group indication is predetermined.

Next, as illustrated in step 2020 in FIG. 20 , the reference signal isreceived, which is transmitted by using a reference signal sequence in areference signal group as indicated by the reference signal groupconfiguration, wherein the reference signal sequence can be multiplexedwith another layer or another user in different reference signal groups.

After the reference signal configuration indication is transmitted tothe UE, the UE will transmit the reference signal using a referencesignal sequence in a reference signal group as indicated by thereference signal group configuration. The eNB may receive the referencesignal from the UE wherein the reference signal sequence can bemultiplexed with another layer or another user in different referencesignal groups.

In addition, it is also possible that the reference signal istransmitted using an aggregated reference signal configuration tosupport more layers. The aggregated reference configuration may be areference signal configuration aggregated from more than oneconfiguration, which may be formed by aggregating the reference signalconfiguration indicated by the reference signal configuration indicationand another reference signal configuration predetermined to be usedtherewith. The another reference signal configuration may be a referencesignal configuration, which is obtained from the reference signalconfiguration indicated by the reference signal configuration indicationbut with a different reference signal group configuration; or may be adifferent reference signal configuration in a cyclic field mappingtable, which is pre-predetermined to be used with the reference signalconfiguration indicated by reference signal configuration indication.

The eNB will demodulate the reference signal in accordance with thereference signal configuration that is transmitted to the UE to learnthe channel condition.

With embodiments of the present disclosure, it provides a new solutionfor reference signal transmission and receiving, in which referencesignal resources are divided into at least two reference signal groupsand reference signals for different layers or users can be multiplexedin different reference signal groups. Thus, more mu-users with unequalallocated bandwidths can be supported without significant channelestimation loss and PAPR loss.

In addition, FIG. 21 further schematically illustrates a block diagramof an apparatus for transmitting a reference signal in accordance withone embodiment of the present disclosure.

As illustrated in FIG. 21 , the apparatus 2100 includes an indicationreceiving module 2110 and a signal transmission module 2120. Theindication receiving module 2110 may be configured for receiving areference signal configuration indication, wherein reference signalresources are divided into at least two reference signal groups, and thereference signal configuration indication indicates a reference signalconfiguration including a reference signal group configuration. Thesignal transmission module may be configured for transmitting thereference signal using a reference signal sequence in a reference signalgroup as indicated by the reference signal group configuration, whereinthe reference signal sequence can be multiplexed with another layer oranother user in different reference signal groups.

In an embodiment of the present disclosure, the at least two referencesignal groups can be multiplexed either in a frequency divisionmultiplexing mode or in a time division multiplexing mode. In thefrequency division multiplexing mode, the at least two reference signalgroups can be further hopped in different symbols.

In another embodiment of the present disclosure, the reference signalconfiguration further may indicate a cyclic shift configuration and anorthogonal cover code configuration. In this case, the reference signalgroup configuration can be implicitly indicated by the cyclic shiftconfiguration or explicitly indicated by a bit in the reference signalconfiguration indication. In addition, whether the reference signalgroup configuration is enabled can be indicated by a bit in thereference signal configuration indication although it is also possibleto be indicated by a separate RRC signaling.

In a further embodiment of the present disclosure, only one referencesignal group can be allowed to be used by a user. In such a case, a partof indices for the cyclic shift configuration can be reserved for alegacy reference signal pattern, a remaining part of the indices can bedivided to at least two groups, each of which is allocated acorresponding one of the at least two reference signal groups. Oralternatively, indices for the cyclic shift configuration can be dividedinto at least two groups, each of which is allocated a corresponding oneof the at least two reference signal groups.

In a still further embodiment of the present disclosure, more than onereference signal group can be allowed to be used by a user.

In a yet further embodiment of the present disclosure, the referencesignal can be transmitted using an aggregated reference signalconfiguration to support more layers, and wherein the aggregatedreference configuration is formed by aggregating the reference signalconfiguration indicated by the reference signal configuration indicationand another reference signal configuration predetermined to be usedtherewith. In this case, the another reference signal configuration maybe a reference signal configuration which is obtained from the referencesignal configuration indicated by the reference signal configurationindication but with a different reference signal group configuration. Oralternatively the another reference signal configuration may be adifferent reference signal configuration in a cyclic field mappingtable, which is pre-predetermined to be used with the reference signalconfiguration indicated by reference signal configuration indication.

In addition, to improve orthogonality between the new user equipment andlegacy user equipment, the apparatus 2100, may further comprise: anoffset increasing module 2130, configured for increasing a cyclic shiftoffset between slots for new user equipment transmitting the referencesignal. Additionally, in order to keep the orthogonality betweendifferent cyclic shifts, the apparatus 2100 may further comprise a shiftdecreasing module 2140 configured for decreasing a cyclic shift for thenew user equipment to keep the orthogonality between different cyclicshifts.

FIG. 22 further illustrates an apparatus for receiving a referencesignal in accordance with one embodiment of the present disclosure. Asillustrated in FIG. 22 , the apparatus 2200 may comprise: an indicationtransmission module 2210 and a signal receiving module 2220. Theindication transmission module 2210 may be configured for transmitting areference signal configuration indication, wherein reference signalresources are divided into at least two reference signal groups, and thereference signal configuration indication indicates a reference signalconfiguration including a reference signal group configuration. Thesignal receiving module 2220 may be configured for receiving thereference signal transmitted by using a reference signal sequence in areference signal group as indicated by the reference signal groupconfiguration, wherein the reference signal sequence can be multiplexedwith another layer or another user in different reference signal groups.

In an embodiment of the present disclosure, the at least two referencesignal groups are multiplexed either in a frequency divisionmultiplexing mode or in a time division multiplexing mode. In thefrequency division multiplexing mode, the at least two reference signalgroups can be further hopped in different symbols.

In another embodiment of the present disclosure, the reference signalconfiguration may further indicate a cyclic shift configuration and anorthogonal cover code configuration. In this case, the reference signalgroup configuration can be implicitly indicated by the cyclic shiftconfiguration or explicitly indicated by a bit in reference signalconfiguration indication. In addition, whether the reference signalgroup configuration is enabled can be indicated by a bit in referencesignal configuration indication although it is also possible to beindicated by a separate RRC signaling.

In a further embodiment of the present disclosure, only one referencesignal group can be allowed to be used by a user. In such a case, a partof indices for the cyclic shift configuration can be reserved for alegacy reference signal pattern, a remaining part of the indices can bedivided into at least two groups, each of which is allocated acorresponding one of the at least two reference signal groups. Oralternatively, indices for the cyclic shift configuration can be dividedinto at least two groups, each of which is allocated a corresponding oneof the at least two reference signal groups.

In a still further embodiment of the present disclosure, more than onereference signal group can be allowed to be used by a user.

In a yet further embodiment of the present disclosure, the referencesignal can be transmitted using an aggregated reference signalconfiguration to support more layers, and wherein the aggregatedreference configuration is formed by aggregating the reference signalconfiguration indicated by the reference signal configuration indicationand another reference signal configuration predetermined to be usedtherewith. In this case, the another reference signal configuration maybe a reference signal configuration which is obtained from the referencesignal configuration indicated by the reference signal configurationindication but with a different reference signal group configuration. Oralternatively, the another reference signal configuration may be adifferent reference signal configuration in a cyclic field mappingtable, which is pre-predetermined to be used with the reference signalconfiguration indicated by reference signal configuration indication.

Hereinbefore, the apparatuses 2100 and 2200 are described in brief withreference to FIGS. 21 and 22 . It is noted that the apparatuses 2100 and2200 may be configured to implement functionalities as described withreference to FIGS. 5 to 20 . Therefore, for details about the operationsof modules in these apparatuses, one may refer to those descriptionsmade with respect to the respective steps of the methods with referenceto FIGS. 5 to 20 .

It is further noted that the components of the apparatuses 2100 and 2200may be embodied in hardware, software, firmware, and/or any combinationthereof. For example, the components of apparatuses 2100 and 2200 may berespectively implemented by a circuit, a processor or any otherappropriate selection device. Those skilled in the art will appreciatethat the aforesaid examples are only for illustration not forlimitation. For example, the number M of the DMRS groups is not limitedto 2 although it is taken an example to describe the present disclosure.In addition, the reference signal receiving and transmitting solutionsare limited only to UL transmission, it is also possible to use for theDL transmission. However, in such a case, unlike the operation asdescribed hereinabove, the eNB will transmit both the reference signalconfiguration indication and the reference signal instead oftransmitting the reference signal configuration indication and receivingthe reference signal; while the UE will receive the RS configurationindication and the reference signal and; demodulate the reference signalbased on the RS configuration as indicated in the RS configurationindication instead of receiving the RS configuration indication andtransmitting reference signal.

Additionally, in some embodiment of the present disclosure, apparatuses2100 and 2200 may comprise at least one processor. The at least oneprocessor suitable for use with embodiments of the present disclosuremay include, by way of example, both general and special purposeprocessors already known or developed in the future. Apparatuses 2100and 2200 may further comprise at least one memory. The at least onememory may include, for example, semiconductor memory devices, e.g.,RAM, ROM, EPROM, EEPROM, and flash memory devices. The at least onememory may be used to store program of computer executable instructions.The program can be written in any high-level and/or low-level compliableor interpretable programming languages. In accordance with embodiments,the computer executable instructions may be configured, with the atleast one processor, to cause apparatuses 2100 and 2200 to at leastperform operations according to the method as discussed with referenceto FIGS. 5 to 20 respectively.

FIG. 23 further illustrates a simplified block diagram of an apparatus2310 that may be embodied as or comprised in a terminal device such asUE for a wireless network in a wireless network and an apparatus 2320that may be embodied as or comprised in a base station such as NB or eNBas described herein.

The apparatus 2310 comprises at least one processor 2311, such as a dataprocessor (DP) and at least one memory (MEM) 2312 coupled to theprocessor 2311. The apparatus 2310 may further comprise a transmitter TXand receiver RX 2313 coupled to the processor 2311, which may beoperable to communicatively connect to the apparatus 2320. The MEM 2312stores a program (PROG) 2314. The PROG 2314 may include instructionsthat, when executed on the associated processor 2311, enable theapparatus 2310 to operate in accordance with the embodiments of thepresent disclosure, for example to perform the method 500. A combinationof the at least one processor 2311 and the at least one MEM 2312 mayform processing means 2315 adapted to implement various embodiments ofthe present disclosure.

The apparatus 2320 comprises at least one processor 2321, such as a DP,and at least one MEM 2322 coupled to the processor 2321. The apparatus2320 may further comprise a suitable TX/RX 2323 coupled to the processor2321, which may be operable for wireless communication with theapparatus 2310. The MEM 2322 stores a PROG 2324. The PROG 2324 mayinclude instructions that, when executed on the associated processor2321, enable the apparatus 2320 to operate in accordance with theembodiments of the present disclosure, for example to perform the method2000. A combination of the at least one processor 2321 and the at leastone MEM 2322 may form processing means 2325 adapted to implement variousembodiments of the present disclosure.

Various embodiments of the present disclosure may be implemented bycomputer program executable by one or more of the processors 2311, 2321,software, firmware, hardware or in a combination thereof.

The MEMs 2312 and 2322 may be of any type suitable to the localtechnical environment and may be implemented using any suitable datastorage technology, such as semiconductor based memory devices, magneticmemory devices and systems, optical memory devices and systems, fixedmemory and removable memory, as non-limiting examples.

The processors 2311 and 3231 may be of any type suitable to the localtechnical environment, and may include one or more of general purposecomputers, special purpose computers, microprocessors, digital signalprocessors DSPs and processors based on multicore processorarchitecture, as non-limiting examples.

In addition, the present disclosure may also provide a carriercontaining the computer program as mentioned above, wherein the carrieris one of an electronic signal, optical signal, radio signal, orcomputer readable storage medium. The computer readable storage mediumcan be, for example, an optical compact disk or an electronic memorydevice like a RAM (random access memory), a ROM (read only memory),Flash memory, magnetic tape, CD-ROM, DVD, Blue-ray disc and the like.

The techniques described herein may be implemented by various means sothat an apparatus implementing one or more functions of a correspondingapparatus described with one embodiment comprises not only prior artmeans, but also means for implementing the one or more functions of thecorresponding apparatus described with the embodiment and it maycomprise separate means for each separate function, or means that may beconfigured to perform two or more functions. For example, thesetechniques may be implemented in hardware (one or more apparatuses),firmware (one or more apparatuses), software (one or more modules), orcombinations thereof. For a firmware or software, implementation may bemade through modules (e.g., procedures, functions, and so on) thatperform the functions described herein.

Exemplary embodiments herein have been described above with reference toblock diagrams and flowchart illustrations of methods and apparatuses.It will be understood that each block of the block diagrams andflowchart illustrations, and combinations of blocks in the blockdiagrams and flowchart illustrations, respectively, can be implementedby various means including computer program instructions. These computerprogram instructions may be loaded onto a general purpose computer,special purpose computer, or other programmable data processingapparatus to produce a machine, such that the instructions which executeon the computer or other programmable data processing apparatus createmeans for implementing the functions specified in the flowchart block orblocks.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of anyimplementation or of what may be claimed, but rather as descriptions offeatures that may be specific to particular embodiments of particularimplementations. Certain features that are described in thisspecification in the context of separate embodiments can also beimplemented in combination in a single embodiment. Conversely, variousfeatures that are described in the context of a single embodiment canalso be implemented in multiple embodiments separately or in anysuitable sub-combination. Moreover, although features may be describedabove as acting in certain combinations and even initially claimed assuch, one or more features from a claimed combination can in some casesbe excised from the combination, and the claimed combination may bedirected to a sub-combination or variation of a sub-combination.

It will be obvious to a person skilled in the art that, as thetechnology advances, the inventive concept can be implemented in variousways. The above described embodiments are given for describing ratherthan limiting the disclosure, and it is to be understood thatmodifications and variations may be resorted to without departing fromthe spirit and scope of the disclosure as those skilled in the artreadily understand. Such modifications and variations are considered tobe within the scope of the disclosure and the appended claims. Theprotection scope of the disclosure is defined by the accompanyingclaims.

What is claimed is:
 1. A method performed by a User Equipment (UE), themethod comprising: receiving an indication from a base station, whichindicates whether or not reference signal resources are divided into afirst demodulation reference signal group and a second demodulationreference signal group, wherein the first reference signal groupcorresponds to a first reference signal sequence, and the secondreference signal group corresponds to a second reference signalsequence, wherein the first reference signal sequence is defined by acyclic shift α of a base sequence r _(u,v)(n) according to:r _(u,v) ^((α))(n)=e ^(jαn) r _(u,v)(n), 0≤n<M _(sc) ^(RS), and thesecond reference signal sequence is defined by a cyclic shift α of abase sequence r _(u,v)(n) according to:${{r_{u,v}^{(\alpha)}(n)} = {e^{j\frac{\alpha}{2}}e^{j\alpha n}{{\overset{¯}{r}}_{u,v}(n)}}},$0≤n<M _(sc) ^(RS); and  generating a reference signal based on theindication.
 2. The method of claim 1, further comprising: transmittingthe reference signal to the base station.
 3. The method of claim 1,wherein the indication which indicates whether or not the referencesignal resources are divided into at least two reference signal groupsis transmitted by radio resource control (RRC) signaling.
 4. The methodof claim 1, wherein the indication to indicate which reference signalgroup is applied is transmitted by Downlink Control Information (DCI).5. The method of claim 1, wherein the reference signal resources aredivided into two reference signal groups.
 6. The method of claim 1,wherein a cyclic shift field corresponding to indices of the secondreference signal group is one of: 000, 001, 010, and 111; and a cyclicshift field corresponding to the first reference signal group is one of:011, 100, 101, and
 110. 7. The method of claim 1, wherein one of thefirst reference signal group and the second reference signal group ismapped to even numbered subcarriers, and the other one of the firstreference signal group and the second reference signal group is mappedto odd numbered subcarriers.
 8. The method of claim 1, wherein if thereference signal resources are divided into the first reference signalgroup and the second reference signal group, cyclic shift α for at leastone of the first reference signal sequence and the second referencesignal sequence associated with layer λ in a slot n_(s) is given asα_(λ)=2πn_(cs,λ)/12N _(cs,λ)=(n _(DMRS) ⁽¹⁾ +n _(DMRS,λ) ⁽²⁾+2n _(PN)(n _(λ)))mod
 12. 9.The method of claim 1, wherein length of at least one of the firstreference signal sequence and the second reference signal sequence ishalf of the length of a legacy Demodulation Reference Signal (DMRS)sequence.
 10. The method of claim 1, wherein length of each of the firstreference signal sequence and the second reference signal sequence isM^(RS) ^(sc) =mN^(RB) ^(sc) /2, wherein N^(RB) ^(sc) is a resource blocksize in frequency domain, expressed as a number of subcarriers, and1≤m≤N^(max,UL) ^(RB) , N^(max,UL) ^(RB) given as a largest uplinkbandwidth configuration.
 11. The method of claim 1, wherein length ofeach of at least one of the first reference signal sequence and thesecond reference signal sequence is M^(RS) ^(sc) =mN^(RB) ^(sc) /2,wherein N^(RB) ^(sc) is a resource block size in frequency domain,expressed as a number of subcarriers, and 1≤m≤N^(max,UL) ^(RB) ,N^(max,UL) ^(RB) given as a largest uplink bandwidth configuration. 12.A method performed by a base station, the method comprising:transmitting an indication to a User Equipment (UE), which indicateswhether or not reference signal resources are divided into a firstdemodulation reference signal group and a second demodulation referencesignal group, wherein the first reference signal group corresponds to afirst reference signal sequence, and the second reference signal groupcorresponds to a second reference signal sequence, wherein the firstreference signal sequence is defined by a cyclic shift a of a basesequence r _(u,v)(n) according to:r _(u,v) ^((α))(n)=e ^(jαn) r _(u,v)(n), 0≤n<M _(sc) ^(RS), and thesecond reference signal sequence is defined by a cyclic shift α of abase sequence r _(u,v)(n) according to:${{r_{u,v}^{(\alpha)}(n)} = {e^{j\frac{\alpha}{2}}e^{j\alpha n}{{\overset{¯}{r}}_{u,v}(n)}}},$0≤n<M _(sc) ^(RS); and  receiving a reference signal based on theindication.
 13. The method of claim 12, wherein the indication toindicate which reference signal group is applied is transmitted byDownlink Control Information (DCI).
 14. The method of claim 12, whereinthe indication which indicates whether or not the reference signalresources are divided into at least two reference signal groups istransmitted by radio resource control (RRC) signaling.
 15. The method ofclaim 12, wherein the reference signal resources are divided into tworeference signal groups.
 16. The method of claim 12, wherein a cyclicshift field corresponding to indices of the second reference signalgroup is one of: 000, 001, 010, and 111; and a cyclic shift fieldcorresponding to the first reference signal group is one of: 011, 100,101, and
 110. 17. The method of claim 12, wherein one of the firstreference signal group and the second reference signal group is mappedto even numbered subcarriers, and the other one of the first referencesignal group and the second reference signal group is mapped to oddnumbered sub carriers.
 18. The method of claim 12, wherein if thereference signal resources are divided into the first reference signalgroup and the second reference signal group, cyclic shift α for at leastone of the first reference signal sequence and the second referencesignal sequence associated with layer λ in a slot n_(s) is given asα_(λ)=2πn_(cs,λ)/12 withN _(cs,λ)=(n _(DMRS) ⁽¹⁾ +n _(DMRS,λ) ⁽²⁾+2n _(PN)(n _(λ)))mod
 12. 19.The method of claim 12, wherein length of at least one of the firstreference signal sequence and the second reference signal sequence ishalf of the length of a legacy Demodulation Reference Signal (DMRS)sequence.